Thermoprotective switch



June 1, 1954 D. F. MoYER 2,680,172

THERMOPROTECTIVE SWITCH Filed NOV. 13, 1952 2 Sheets-Sheet l INVENTOR. @A V/o F. M0 f5-A2 June l, 1954 v D, F, MOYER 2,680,172

THERMOPROTECTIVE SWITCH Filed Nov. 13, 1952 2 Sheets-Sheet 2 w E f T 6l?? /a 4f INVENTOR. 0,4 W0 No m55 MMM Patented June l, 1954 UNITED STATES PATENT OFFICE 2,680,172 'THERMOPROTECTIVE SWITCH David F. Moyer, Dayton, Ohio, assignor `to 'General Motors Corporation, Detroit, Mich., a corporation -of Delaware Application November 13, 1952, Serial No. 320,275 7 Claims. (Cl.-200'-116) 1 'Ihis invention relates to 'an improved protective control device .for automatically opening the 'electric circuit to an electrical device, vsuch 'as Vanelectric motor, whenever over-loads occur on a'protective control device incorporating the features of the aforesaid object wherein an Velectric shunt is provided around the current-sensitive tripping mechanism of the device to provide for usage of a single device on a wide range of current loads.

Further objects `and advantages of the 'present invention will be apparent from the following description, reference being had to the accompanying ldrawings wherein a preferred embodithe electrical device. 5 ment of the present invention is clearly shown.

An 'object of the invention is `to provide a pro- AIn the drawings: tective control `device that has 'a short time Ilimit Fig. l Tis aside elevational view of a protective for opening an electric circuit onder overload control device constructed in accordance `with conditions of an electrical apparatus, and 'which the invention and yincluding a'diagr'ammatic elecdevice `can be utilized with electric apparatus tric circuit in which to provide suitable protecovera Wide range of 'current usage. tion for an lelectric motor;

In previous yprotective control devices it has Fig. -2 is acrosssectional view taken along the been considered lessential to vary the construclines '2-2 oi Fig. 3, lbut illustrating certain rof tion of the heat-sensitive elementof a protective the Lpart's of the device vin 1dotand-dash 'line for control device so that it might accept varying the purpose of clarity; current loads. Thus, it yhas been the usual prac- Fig. '3 is a fcro'ss lsectional vieiv taken `along the tice to calibrate carefully the electric heaters or line 3-3 of Fig. l; vother current-sensitive devices used in protective Fig. 4 Yis 'an veleva-tional view of Aone of the afd- `control devices so that they could be matched justment plates of the device 'which affects 'the accurately to the current 'rating of the electrical 2o current rating of the device;

,device to give the desired degree of overload Fig. v5 is an elevational View of another 'a'dprotection to the electrical device. justment pla-te of the device;

In this invention, however, the apparatus is Fig. 6 is a side elevational view of the plate constructed and arranged in a manner that a inFig. 5. single electrical component that is current sensi- The apparatus of this invention -incl'ude's a tive can be used to give satisfactory overload housing lllv constructed lof electrical insulating protection to a Wide range of electrical devices material. The housingA |-0 has a chamber Il drawing widely varying currents. that receives the actuating mechanism of the The foregoing is accomplished yin this -invendevice. tion -by constructing the apparatus to vary the The actuating mechanism consists of a rod mechanical relationships of the tripping mechan- I -2 journaled in the walls i3 and I4 o'f the housical components of the protective control device ing |11, the rod lf2 protecting 'across the chamber while retaining the tripping time relatively il. One end of the rod I Zcarries a contact bar constant, thus eliminating the necessity of acl5 that is urged against a shoulder 16 by means curately calibrating heat-sensitive or current of a compression spring Il. A finger button Hl sensitive devices that vary widely in manu-facis mounted `on the end of the rod l2 and retains turing tolerances. f the spring H in position between the button I-8 It is, therefore, an object of this invention to and the con-tact bar l5. provide a protective Control del/10. particularly "Contacts 19 and 21) are secured to the Wall i3 for electric motors, whereinA the position of the l 0f the housing I0 for engagement by the contact mechanical components of the tripping mechabar |5 whereby to conduct current to an dem nismof the device can have their relative positi-ical apparatus, .gu-Ch as an 'electr-@ moi-,M tions changed to effect substantially constant The ma |2 has a reduc-ed diameter extension time lagvin operation oLf the tripping mechanism 2| that .ext-ends 'mugh an ope-ning -2'2 in an undelf dlerent Currn" usage 'arm means 2-3, the armvm'e'ans 23 forming one It 1s a further object of -the lnventlOIl t0 C- of th mechanical components 0f a tripping cmhsh thi. aforesaq (bflfect-b1yt-a1temghth mechanism. The rod portion 2l engages the plvo comme 1099i a rlp e er le a we o a ea" arm 23 at opposite sides of the opening 2.2, the o1 current sens1t1ve device. .2,3 id. b t' en kn-f ed .es 24 dgl.. a

It is also an object of the invention to provide arm r mg e We 1 e g an p10` vided on the rod portion 2|.

The arm `23 is supported at one end thereof by a pivot pin 26. The pivot pin 28 is in vturn journaled in an opening 21 provided in a mounting' plate member 30.

The mounting plate 30 is the second of two mounting plates that cooperate to support the pivot 26 in a controlled linear position relative to a heat-sensitive bimetal detent member 3 i. The first mounting plate member is the plate 32 supported on the housing il).

The mounting plate 32 is movably supported on the housing lll, with the iixed pivot pin 33 secured to a wall 3d of the housing. (See Fig. '3.) The plate 32 is rotatable about the fixed pivot 33 and is secured immovably relative to the housing I@ by means of a screw 35 in threaded engagement with the housing wall 34. An enlarged opening 36 is provided in the plate 32 to provide for limited rotative movement of the plate 32 about the fixed pivot pin 33.

The second mounting plate 30 has an opening 31 that fits over the fixed pivot $23. The plate 3G also carries a screw 38 that extends through an opening 39 into engagement with the threaded boss 40 of the plate 32, whereby to predominately position the plate 3a relative to the plate 32, and to provide for removal of the plate from the plate 32 under conditions and for reasons hereinafter described.

The arm 23 is spring urged in a clockwise direction (see Fig. 2) about the pivot 26 by means of a spring 4l.

A current heat-sensitive detent member 3l is secured to the housing I by means of a fastening screw 28 and a conductor lug t3. The free end 44 of the currentensitive, bimetal element 3l is attached to a flexible electric lead lle that in turn is attached to a conductor lug 46. Thus, electric current is carried through the element 3| for rendering it current-sensitive to heating under the load drawn by the electrical device in circuit with the protective control device.

When the protective control device is in circuit closing position, the parts thereof assume the relative positions shown in Fig. 1 with the free end 4l of the arm 23 being engaged by the free end 44 of the detent 3| to hold the contact bar i upon the contacts i9 and 20.

With the protective control device in the position illustrated in Fig. l an electric circuit is closed through the contacts I9 and 20 to an electric motor 5@ diagrammatically illustrated in the Wiring circuit of Fig. l.

The electric motor 50 consists of a running' winding 5l and a starting winding 52. A speed responsive switch 53 is placed in circuit with the starting winding 52 for opening the starting winding when the motor approaches running speed.

Electric circuit to the motor 5G is thus made through the protective control device through the electric line 55, contacts i9 and 2Q, line 56,

detent member 3l, lead 45 and line 51 to the opposite side of the line 58.

In operation, when the motor 5E becomes overloaded for any reason, current carried by the detent member 3| causes excessive heating of the member 3l whereby it bends downwardly (see Figs. l and 2) to cause release of the arm 23. The arm 23 moves in a clockwise direction about pivot 26 as urged by the spring A! to cause movement of the rod l2 in a left-hand direction and thereby open the circuit through the contacts I3 and 20. rIhis results in breaking the circuit to the motor 50, or other electrical device arranged in series with the protective device.

The protective control device is manually reset after the overload is removed from the motor, removal of the overload allowing the bimetal 3l to cool, by moving the rod l2 in a right-hand iii) direction to reset the tripping mechanism comprising the arm 23 and the member 3 i.

The bimetallic detent member 3l when constructed to determined dimensions and of determined materials has a predetermined rate and extent of movement resulting from heating thereof to predetermined values. This is an accepted electrical characteristic of bimetal elements and therefore any given current-sensitive or heat-sensitive, bimetallic element will have the free end thereof moved a predetermined distance over a predetermined time interval when heat is applied to the bimetal at a given rate, either by an external source or by electric current now through the bimetal. Thus, any specic mechanical arrangement of the bimetal element with a tripping arm can provide for only one timed release of the armunder any given set of circumstances, To provide for the same tripping time under a different current. load requires an interchange of bimetal elements having different electrical characteristics. In this invention, however, a single bimetal element is used to carry a plurality of current values and still maintain substantially the same tripping time to provide overload protection for electrical devices having widely varying current ratings.

This is accomplished in the structure of this invention by controlling the linear dimension between the pivot 25 and the free end 44 of the bimetal 3l. When the bimetal element 3i is at rest in its normal unfiexed position, the pivot 2G can be positioned from the free end ylil of the bimetal 3i to provide for protection of an electrical device having low current rating. As the current rating of the device to be protected increases the pivot 26 of the arm 23 is moved linearly of the free end 44 of the bimetal 3l thereby giving a greater extension of the arm 23 beyond the free end of the bimetal member. However, since the current rating of the device being protected is increased, there will be a greater rate of movement of the bimetal member 3i because of the increased current now through the member 3l, resulting in a tripping time of the protective device of substantially the same value as when used in circuit with an electrical device of lower current rating.

The bimetal member 3i while having a rate of movement determined by the current flow through it which increases with increasing current flow, also has a relative maximum rate of movement beyond which increasing current flow through the bimetal has substantially no effect. Therefore, bimetal elements have a maximum utility beyond which they are no longer eiiective for response to increased current iiow. Also, there is a maximum safe current flow that can be carried by a specific bimetal element. However, in this invention the eiectiveness of the bimetal member 3l is retained for current ratings beyond its normal maximum safe current load by placing an electrical shunt iii] in parallel with the bimetal member 3l to carry a part of the current drawn by the electrical apparatus, such as the motor Eil. The electrical shunt thereby relieves the bimetal member 3l from a part of the total current carried. The arrangement is such that the maximum current carried by the bimetal is no more than the maximum safe current to which it is normally responsive at a maximum rate of movement. For example, the bimetal element 3| when used alone, will provide for thermal overload protection for electrical loads rated from about 4.8 amperes to 13 amperes. By placing an electrical i shunt El) 4in parallel with the bimetalmember 3| so that the bimetal carries only one-third-of the total current, the bimetal element can be madev to functionv at substantially the same rates `as previously through a new range of' from about 14 amperes to 49 amperes.

To accomplish changes in current rating of the protective control device, the mounting plate 30 is one of a series of plates in which each plate has the opening ily for the pivot 26' positioned about the opening 3! at a different radial` angle, for'example, openings 65 and tt, shown in dotted lines in Fig; 4, to provide for different linear displacement of the pivot 26 relative to the free end 44 of the bimetal element 3l. Thus, toadapt the protective control device of this invention to vdifferent current rating of electrical apparatus, it is merely necessaryl to remove the plate 30 from the device and replace itl with another identical plate having the pivot opening 2l placed linearly diierent relative to the free end M of the bimetal 3|.

The plate 32 provides for a factory adjustment of the protective control device. This is accomplished by placing a plate 3i) in position upon the plate 32 with what may be termed a zero rating to which all protective devices are factory adjusted. The zero rating of the factory adjustment is occasioned by rotating plate 32-on the pivot pin 33 to adjust the free end il of the arm 23 relative to the free end 44 of the bimetal 3l whereupon the screw 35 is tightened and soldered to prevent subsequent tampering. Rating readjustment of the protective control device to match theV current rating of an electrical device to be controlled thereby is then made by removing the factory adjustment plate 3i! and replacingthe same with a previously prepared rating plate 30 having a predeterminately positioned pivot open ing 2T to establish a predetermined displacement between the pivot 26 and the free ended of the -bimetal 3l to give a predetermined time lag to the tripping mechanism according to the current drawn by the electrical device to be controlled.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood thatv other forms might be adopted.

What is claimed is as follows:

1,. A protective control device for automatically opening an electric circuit to an electrical device, comprising in combination, shiftable circuit breaking for closing an electric circuit to render an electrical device operative, arm means engageable with said circuit breaking means to render the same active, pivot means for pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means to provide for actuation of said circuit breaking means, mounting plate means on said device carrying said pivot means, and locating means on said device predeterminately positioning said plate means on said device and relative to said detent means, said mounting plate means being removably attached to the control device for interchange with other like mounting plate means interchangeably attachable on said device but having the pivot carrying means thereof disposed therein linearly different relative to said detent means whereby to regulate the tripping position of said arm means relative to said detent means.

2. A protective control device for automatically opening-an electric circuit to; anelectrical device, comprising in combination, shi'ftable. circuit breaking-means fork closing an electric circuit to render an electrical device operative, arm means` engageable with said circuit breaking means to render the same active, pivot means forI pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means to provide for actuation of said circuit breaking means, and mounting means carrying said pivot means, said mounting meansA comprising a iirst mounting plate movably supported on said device for movement relative to said detent means and a second mounting plate removably attached to said rst member and having means carrying said pivot means whereby said mounting plates predeterminately position said pivot means rela.- tive to said detent means to control the tripping position of said arm means relative to said detent means.

3. A protective control device for automatically opening an electric circuit to an electrical device, comprising in combination, shiitable circuit breaking means for closing an electric circuit to render an electrical device operative, arm means engageable with said circuit breaking meansV to render the same active, pivot means for pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means toy provide for actuation of said circuit breaking means, and mounting means carrying said pivot means, said mounting means comprising a rst mounting plate movably supported on said device for movement relative to said detent means and avsecond mounting plate removably attached to saidl iirst mounting plate and having means carrying said pivot means whereby said mounting plates co-operate to predeterminately position said pivot means relative to said detent means to control the tripping position oi said arm means relative to said detent means.

4.. A protective control device for automatically opening an electric:v circuit to anelectrical device,

comprising in combination, shiitable circuit breaking means for closing an electric circuit to render an electrical device operative,` arm means engageable with said circuit breaking means to render the same active, pivot means for pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means to provide for actuation of said circuit breaking means, and mounting means carrying said pivot means, said mounting means comprising a rst mounting plate supported upon a iixed pivot on said device and rotatable about said fixed pivot toward and away from said detent means, fastening means between said first plate and said device for holding said rst plate immovable on said device, and a second mounting plate removably attached to said iirst plate and having means carrying said pivot means whereby said mounting plates cooperate to predeterminately position said pivot means relative to said detent means to control the tripping position of said arm means relative to said detent means.

5. A protective device for automatically opening an electric circuit to an electrical device, comprising in combination, shiftable circuit breaking means for closing an electric circuit to render an electrical device operative, arm lmeans engageable. with said circuit breaking means to render the same active, pivot means for pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means to provide for actuation of said circuit breaking means, and mounting means carrying said pivot means, said mounting means comprising a rst member movably supported on said device for movement relative to said detent means and a second member removablyT attached to said rst member and having means carrying said pivot means whereby said mounting members predeterminately position said pivot means relative to said detent means to control the tripping position of said arm means relative to said detent means, said second mounting member being interchangeably attachable in identical position on said rst member with other like mounting members having the pivot carrying means thereof disposed linearly different relative to said detent means whereby to regulate the tripping position of said arm means relative to said detent means by the linear position of said pivot means relative to said detent means.

6. A protective control device for automatically opening an electric circuit to an electrical device, comprising in combination, shiftable circuit breaking means for closing an electric circuit to render an electrical device operative, arm means engageable with said circuit breaking means to render the same active, pivot means for pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means to provide for actuation of said circuit breaking means, and mounting means carrying said pivot 'l means, said mounting means comprising a first mounting plate supported upon a Xed pivot on said device and rotatable about said fixed pivot toward and away from said detent means, fastening means between said iirst plate and said de- 0 vice for holding said first plate immovable on said device,v and a second mounting plate removably attached to said rst plate and having means carrying said pivot means whereby said mounting plates cooperate to predeterminately position said pivot means relative to said detent means to control the tripping position of said arm means relative to said detent means, said second mounting plate being interchangeably attachable in identical position on said first mounting plate with other like mounting plates having the pivot carrying means thereof disposed linearly different relative to said detent means whereby to regulate the tripping position of said arm means relative to said idetent means by the linear position of said pivot means relative to said detent means.

7. A protective control device for automatically opening an electric circuit to an electrical device, comprising in combination, shiftable lcircuit breaking means for closing an electric oircuit to render an electrical device operative, arm means engageable with said circuit breaking means to render the same active, pivot means for pivotal mounting of said arm means, heat sensitive detent means engageable with said arm means retaining the same in position for closing of said circuit breaking means and providing tripping means for release of said arm means to provide for actuation of said circuit breaking means, and mounting means lcarrying said pivot means, said mounting means comprising a nrst mounting plate supported upon a iixed pivot on said device and rotatable about said fixed pivot toward and away from said detent means, fastening means between said first plate and said device for holding said rst plate immovable on said device, and a second mounting plate removably attached to said rst plate and predeterminately positioned thereon by said fixed pivot and an attachment member and having means carrying said pivot means whereby said mounting plates cooperate to predeterminately position said pivot means relative to said detent means to control the tripping position of said arm means relative to said detent means.

References Cited in the file of this patent UNITED STATES PATENTS 

